1. Field of the Invention
The present invention relates to therapeutic medical apparatus, systems, devices and/or methods, and more particularly, to apparatus and methods for using neural stimulation to alleviate the symptoms of movement disorders, such as those associated with Parkinson's disease, essential tremor, dystonia, and Tourette's syndrome, including tremor, bradykinesia, rigidity, gait/balance disturbances, and dyskinesia, as well as sleep disorders such as REM sleep behavior disorder and restless leg syndrome.
2. Technical Background
There has been tremendous growth and active research into disease modifying agents of Parkinson's disease (PD) as well as pharmaceutical and surgical treatments for associated motor symptoms. PD, a neurodegenerative disorder that affects the motor system, is characterized by tremor, slowed movements (bradykinesia), and rigidity. With approximately 1.5 million Americans diagnosed with PD and over 50,000 new cases each year, the need for intervention to both treat the symptoms and alter disease progression cannot be understated. Overnight transcranial direct current stimulation (tDCS), which provides a noninvasive painless electrical polarization to the cerebral cortex, could provide a non-pharmaceutical and non-surgical therapeutic option to complement current treatments for PD motor symptoms and related sleep disturbances.
PD is caused by a loss of dopamine-producing neurons in the substantia nigra, but the exact reason for neurodegeneration remains unknown. A current trend in the treatment of diseases identified as being associated with the central nervous system is the stimulation of target areas of the central nervous system to effect therapeutic benefit. Such stimulation has been accomplished with, for example, implanted electrodes that deliver electrical stimulation to target brain regions; one class of electrical neural stimulation devices has been categorized under the name “deep brain stimulation” (DBS). Although the exact neurological mechanisms by which DBS therapies succeed are complex and are not yet fully understood, such therapies have proven effective in treating Parkinson's disease motor symptoms (such as tremor, bradykinesia, rigidity, and gait disturbances), and investigation into the use of DBS for the treatment of this and other neurological and mental health disorders, including major depression, obsessive-compulsive disorder, tinnitus, obesity, criminal tendencies, and antisocial disorders, is ongoing.
Typically, medication for Parkinson's disease (PD) consists of Levodopa to alleviate symptoms. Over time, however, the medication has reduced efficacy and shows increased occurrence of side effects such as dyskinesias. Once side effects outweigh benefits, subjects consider deep brain stimulation (DBS). An electrode/wire lead is implanted in a specific location in the brain which shows hyperactivity in PD subjects and is sensitive to electrical stimulation. PD target sites are the subthalamic nucleus (STN) or globus pallidus internus (GPi). The essential tremor and Parkinson tremor target site is generally the ventral intermedius nucleus of the thalamus (VIM). Electrical pulses characterized by amplitude (volts), current (amps), frequency (Hz), and pulse width (microseconds) are regulated by an implantable pulse generator (IPG) placed beneath the skin on the chest. Stimulation affects motor symptoms on the contralateral side, i.e., right side tremor will be treated on the left brain. After a subject has been implanted and recovered, programming sessions will fine tune stimulation settings described above in order to minimize symptom severity, minimize side effects, and maximize IPG battery life span. Although medication is not eliminated, it is typically reduced significantly. DBS efficacy decreases over time as the body adjusts to stimulation and protein buildup around electrode lead attenuates electrical field. Programming sessions are required throughout the subject's lifetime, though the frequency of adjustments are typically greater at first.
A typical implanted DBS stimulation lead consists of a thin insulated needle comprising four platinum/iridium electrodes spaced 0.5 or 1.5 mm apart along the length of the lead. One or multiple leads may be implanted in a target brain region or regions to provide symptom-inhibiting high-frequency stimulation, although some research suggests that excellent results can be achieved even when the lead is implanted distant from a target region. A DBS lead is connected to an implantable pulse generator (IPG), which serves as a controller and power source, via an extension cable tunneled subcutaneously to a subcutaneous pocket in the chest or abdominal cavity. The IPG typically includes a battery and circuitry for telemetered communication with an external programming device used to adjust, or “tune,” DBS lead stimulation parameters, which may include stimulation frequency, amplitude, pulse width (or wavelength), and contact configuration (that is, the selection of which electrodes are utilized from among the four electrodes available on a lead, and, if two or more electrodes are active, the relative polarity of each). These parameters are initially set during implantation surgery and are then further fined-tuned in the outsubject clinic or in a doctor's office following surgery to maximize therapeutic benefit and minimize undesirable stimulation-induced side effects. The first such tuning session usually takes place several weeks following implantation surgery, after the subject has recovered and inflammation at the lead placement site has subsided.
While existing drug and DBS treatments do alleviate motor symptoms, new data has documented that tDCS has therapeutic potential in PD both acutely and chronically. tDCS is a noninvasive brain simulation modality in which direct current is steadily applied via electrodes on the surface of the scalp. tDCS polarizes the brain using weak direct currents that are applied via scalp electrodes. Finite element models (FEM) show that current densities in the cortex resulting from tDCS are 2-3 orders of magnitude lower than action potential thresholds, thus, tDCS does not stimulate cortex, but rather modulates cortical excitability. Fregni et al. found that Unified Parkinson's Disease Rating Scale (UPDRS) scores improved significantly after anodal stimulation to primary motor cortex (M1) (p<0.001), F. Fregni et al., Noninvasive cortical stimulation with transcranial direct current stimulation in Parkinson's disease, Mov. Disord. 2006 October; 21(10):1693-1702. The current standard in evaluating the severity of movement disorder symptoms in Parkinson's disease is the Unified Parkinson's Disease Rating Scale (UPDRS) used to score motor tests, many of which involve repetitive movement tasks such as touching the nose and drawing the hand away repeatedly, or rapidly tapping the fingers together. A battery of exercises, typically a subset of the upper extremity motor section of the UPDRS, is normally completed during DBS lead placement surgery and subsequent programming sessions to evaluate performance while a clinician qualitatively assesses symptoms. Each test is evaluated by a clinician based solely on visual observation and graded on a scale that ranges from 0 (normal) to 4 (severe). More recently, Benninger et al. found that tDCS did not significantly improve overall UPDRS scores; however, bradykinesia, the primary complaint in many PD subjects, did significantly decrease (p<0.0001). D. H. Benninger et al., Transcranial direct current stimulation for the treatment of Parkinson's disease, Journal of Neurology, Neurosurgery & Psychiatry. 2010 September; 81(10):1105-1111. The fact that Chen states that tDCS as a treatment for PD is “not ready for prime time,” but does emphasize that pilot studies are needed and “useful adjunctive treatments are clearly welcome,” serves to point out that tDCS for movement disorder therapy is far from known in the art, but has shown potential for utility in this field. R. Chen, Transcranial direct current stimulation as a treatment for Parkinson's disease—interesting, but not ready for prime time, Journal of Neurology, Neurosurgery & Psychiatry. 2010 June; 81(10): 1061-1061. In addition to likely improving motor function in PD subjects, tDCS has been established and shown to have efficacy in various other fields, such as to aid in rehabilitation after stroke, improve motor learning in healthy adults, improve memory in subjects with Alzheimer's disease, improve mood in subjects with major depression, and improve memory during slow-wave sleep. Recent studies have shown that DBS during sleep either directly or as a function of increased mobility improves sleep quality in PD subjects, suggesting the tDCS may too improve sleep quality. A. W. Amara et al., The effects of deep brain stimulation on sleep in Parkinson's disease, Ther. Adv Neurol. Disord. 2011 January; 4(1):15-24.
Unlike other noninvasive stimulation modalities such as transcranial electrical stimulation (TES) and rapid transcranial magnetic stimulation (rTMS) that can be costly, painful, and cause side effects including seizures and psychotic symptoms, tDCS is painless, poses few side effects, and is ideal for home use since it can be provided in an inexpensive and compact package. The only sensation from tDCS is tingling during stimulation onset. This in sharp contrast to rTMS, which induces a strong scalp sensation along with facial and scalp muscle twitches. Additionally, rTMS systems are extremely bulky, require a large power supply, cost $20,000-$100,000, and are not suitable for home use. Conversely, the disclosed tDCS system will be specifically designed for home use and be much more cost effective.
In light of the above, it is therefore an object of the present invention to provide a noninvasive movement disorder therapy system, and methods of using the same, which can reduce the severity and frequency of a subject's symptom occurrence, improve the subject's sleep quality, and improve the subject's overall quality of life while reducing the amount of the subject's waking life required to receive such therapy.